Known in the prior art are various visual and photoelectric methods for measuring optical quantities. Known in the prior art also are many apparatuses for measuring the light absorption (spectrophotometers), light scattering (nephelometers), circular birefringency (spectropolarimeters) and circular dichroism (spectrodichrographs). With respect to the measurements of linear birefringency (double refraction) and linear dichroism, no instruments are now to our best knowledge produced on the commercial basis. There exist only some laboratory devices for these measurements built in scientific institutes where they are needed.
Physical principles underlying these methods and instruments are specific for the measured quantity. Therefore each of these instruments provides the possibility to measure only one of the aforementioned optical quantities. Different instruments are required to measure various quantities.